1. Field of Invention
The present invention relates to a liquid crystal display (LCD) element and, in particular, to an LCD element with a defect repairing function. The invention also discloses a defect repairing method.
2. Related Art
With the merits of small volume and light weight, liquid crystal display (LCD) holds the edge in the market of portable display devices and smallspace application displays. Among all, the thin film transistor liquid crystal display (TFT-LCD) is the most favorable device. The device is using the field effect transistors to control the voltage applied to the liquid crystal film layer so as to control the orientation of liquid crystal molecules, thus adjusting the penetration of light through the liquid crystal layer. With the utilization of filters, a screen is able to display various colors and brightness.
FIG. 1A shows a standard circuit layout of a thin film transistor liquid crystal display (TFT-LCD) panel. A series of parallel scan lines 10 and a series of parallel data lines 20 are orthogonal to each other and not connected. They connect to a control electrode 12 and a control electrode 22, respectively, and separate the display panel into an array composed of pixels. Each pixel in the array has a field effect transistor (FET) 30, a liquid crystal capacitor 40 and a storage capacitor 50. Each FET has a gate, a drain and a source, wherein the gate connects to the corresponding scan line, and the drain connects to the corresponding data line. The liquid crystal capacitor 40 and the storage capacitor 50 are connected in parallel between the drain of the FET 30 and the ground.
In the conventional LCD elements, a detailed standard layout of each pixel is shown in FIG. 1B. The conduction areas 32, 34, 36 are the gate, source, and drain of the FET 30, respectively. The area 38 is the semiconductor channel of the transistor 30. The FET drain 36 connects to a transparent electrode plate 45, which functions simultaneously as the electrodes for the liquid crystal capacitor 40 and the storage capacitor 50. The transparent electrode plate 45 is usually made of indium tin oxide (ITO). A storage electrode plate 52 is installed underneath the transparent electrode plate 45 with a dielectric layer inserted between (not shown) so as to form a storage capacitor 50. The liquid crystal capacitor 40 is formed above the transparent electrode plate 45.
With the technology development of displays heading toward high screen quality and large sizes, manufacturers have to use narrower line width and smaller pixel sizes to make longer signal transmission lines (including scan lines and data lines) on the large-scale panels. Under this situation, such problems as uneven line width distribution and broken lines are likely to happen. It is also likely to have short circuits because of holes between separated electrodes, e.g., between the upper and lower electrode plates of the storage capacitor 50 (the transparent electrode plate 45 and the storage electrode plate 52), between the FET gate 32 and the source and drain 34, 36, or between channels 38. Broken signal lines will result in line defects since an entire row of pixels cannot receive control signals. Short circuits of electrode plates will cause point defects as the pixels cannot react to the voltage. Both of them have bad influence on the quality and the production yield of the display panels.
FIG. 2A shows a pixel array circuit for repairing line defects in the prior art. The basic circuit layout is the same as in FIG. 1A, except that the array border is surrounded with a spare line 80 over three sides. The spare line 80 is floating and striding over the data lines and scan lines, with a dielectric layer between. Its cross-sectional view is shown in FIG. 2B. The conduction layer 210 on the substrate 200 representing the signal lines 10 on the lower layer, and the conduction layer 230 representing the spare line 80 on the upper layer are segregated by a dielectric layer 220 inserted between. When no defect is detected in the display panel, the spare line is maintained in the default configuration. However, when one of the data lines is detected to have a line defect, i.e., the data line is broken because of discontinuity, then the spare line overlapping on the defective data line is melted (usually using a high energy laser) so that the conductive material can pass through the dielectric isolation layer to form a contact window 240 with the conductive wire on the lower layer. When both ends of the defective data line are connected to the conduction layer 210 by melting, the spare line 80 can replace the broken data line and transmit control signals to transistors.
Nevertheless, this line defect repairing design still has its drawbacks. The spare line is so long and strides over so many data lines and scan lines that parasitic capacitance effect occurs during the control signal transmission. The signal received by the transistors will be decreased and seriously distorted, resulting in bad screen images. In addition, this surrounding spare line design cannot repair multiple defects, such as line defects indicated above. To further increase the product quality and manufacturing yield and to control production costs, it is crucial to develop a better defect repairing method.
In view of the foregoing bad defect repairing ability in conventional liquid crystal display (LCD) panel, it is an object of the invention to provide an LCD element with good defect repairing ability and the corresponding defect repairing method capable of repairing line defects and point defects due to broken circuits and short circuits, respectively.
To repair the line defects, the invention provides a circuit design of a single pixel having multiple scan lines and multiple data lines, with separate spare lines installed between. When a broken circuit occurs to any data line or scan line, the spare line is electrically welded to connect to the broken circuit, thereby forming the shortest connection path. This can minimize the signal attenuation due to long wiring and is suitable for multiple line defect repairs.
To repair point defects, the invention provides a circuit design of a single pixel having multiple subpixel electrodes, with spare conduction ports installed between. With the application of welding and connecting joints, the defective electrode can be readily separated once any subpixel has a defect. The spare conduction port for connection is melted for connection, and the resource of other subpixels will be used to support and compensate for the defective subpixel in an attempt to decrease the loss in screen image signals.